# Mechanical Nitriding of Titanium and Its Alloys as a Feedstock for the Additive Manufacturing of Functionally Graded Materials

## TL;DR

A new method creates a titanium nitride coating on titanium powders for use in 3D printing advanced biomaterials.

## Contribution

A novel self-shearing reactive milling method is introduced to coat titanium powders with TiN without grinding media.

## Key findings

- TiN coatings were formed on Ti, Ti6Al4V, and Ti-5553 powders with thickness around 500 nm.
- X-ray diffraction confirmed TiN phase only in Ti6Al4V after 10 h of milling.
- Raman spectroscopy detected TiN even at early milling stages, and spherical shape was preserved.

## Abstract

TiN coatings were obtained on the surface of the titanium and its alloys powders.

Self-shearing reactive milling under nitrogen pressure was performed.

The thickness of TiN coatings was in a nanometric scale.

No grinding media was used during the milling processes.

The spherical shape of the powder particles after milling was preserved.

This work focuses on obtaining a titanium nitride coating on the surfaces of titanium and its alloy powders using a novel method, self-shearing reactive milling, under a nitrogen pressure of 50 bar. The Ti, Ti6Al4V, and Ti-5553 spherical powders were milled for up to 10 h at ambient temperature without grinding balls. As a result of the experiments, a thin, brittle TiN coating formed on the powders’ surfaces. The cross-sections of the milled powders reveal that the TiN layer thickness is in the nanometer range (about 500 nm). By analyzing the sequence of X-ray diffraction patterns, it is evident that only for the Ti6Al4V powder milled for 10 h, two peaks are observed that can be attributed to a TiN phase. On the other hand, Raman spectroscopy revealed characteristic TiN spectra even for samples collected at the initial stage of self-shearing reactive milling. An important aspect of the experiment was the preservation of the spherical shape of the milled powders, which makes them a potential feedstock for additive manufacturing of functionally graded biomaterials.